Coatings having specific release properties toward adhesives are widely used. Polydimethylsiloxanes and polymers containing predominately dimethylsiloxane units provide very low release coatings, e.g., they exhibit release of 4 to 16 grams per centimeter of width, for products such as labels or large sheets which contain normally tacky and pressure-sensitive adhesives. These polymers are less useful as release coatings on the back surface of adhesive tape (back surface coating of adhesive tape is known as "low adhesion backsize" (LAB)) because their low release force can cause roll instability. LABs for tapes in roll form ideally exhibit release toward the adhesive of about 60 to 350 g/cm of width. Polymers with higher release values make it increasingly difficult to use the tape and delamination of the adhesive from the substrate often can result. Coatings having release values less than 60 g/cm of width are useful as components for release liners. Many non-silicone polymers, e.g., urethanes, find use as low adhesion backsizes for pressure-sensitive tapes because of their much higher release force than the polydimethylsiloxanes, typically greater than 200 g/cm width. Such non-silicone LAB coatings are exemplified in U.S. Pat. Nos. 2,607,711, 2,876,894 and 3,342,625.
For products such as tapes and liners, coatings having specific release properties toward adhesives, which are intermediate between those of the polydimethylsiloxanes and conventionally used non-silicone LAB coatings, are highly desired. Many previous attempts to provide such coatings by modification of polydimethylsiloxanes or blending them with less effective release material, as disclosed in, for example, U.S. Pat. Nos. 3,328,482, 3,527,659, 3,770,687 and 3,891,745, have not met with total success because of many problems such as: (1) incompatability of components causing extensive migration of the silicone to the surface, (2) contamination of the adhesive with low molecular weight components giving adhesion loss, (3) nonreproducibility, e.g., inability to consistently achieve the desired release level, and (4) use of excessively high cure temperatures causing deterioration of the heat-sensitive substrate or tape backing.
Coating compositions exhibiting intermediate release properties towards adhesives, provided by reaction of an isocyanate with a hydroxyl or amine-containing organosiloxane, are described in U.S. Pat. No. 3,997,702.
Epoxypolysiloxanes have been previously used as polymer components to impart water repellency to textile and paper (U.S. Pat. Nos. 4,046,930 and 3,055,774), as treating agents for filling synthetic fiber (U.S. Pat. No. 4,062,999), as adhesion additives (U.S. Pat. No. 4,033,924), and in pre-crosslinked compositions, in which the epoxy group is present on a cycloalkylgroup, for rendering surfaces non-adherent (U.S. Pat. Nos. 4,279,717 and 4,421,904), in an abrasion-resistant layer in a multilayered sheet (U.S. Pat. No. 4,337,107), and in an abrasion resistant coating (U.S. Pat. No. 4,343,855).
Epoxypolysiloxanes have also been used in coatings for release liners. In U.S. Pat. No. 4,313,988 there are described differential release liners and low adhesion backsizes for tapes comprising cured epoxypolysiloxanes as represented by the formula ##STR1## wherein
R is a lower alkyl of one to three carbon atoms,
R.sup.1 is a monovalent hydrocarbyl radical of 4 to 20 carbon atoms,
E is a monovalent epoxy-containing hydrocarbon radical,
M is a silyl group R.sub.3 Si--, R.sub.2 R.sup.1 Si--, or R.sub.2 ESi--,
a is 5 to 200,
b is 0 to 20% of a,
a+b is 5 to 200,
c is up to 20% of a+b and
n is 1 to 5.
Also, ultraviolet radiation curable compositions for controlled release comprising epoxy functional dioganopolysiloxanes in which up to 20% of the groups are epoxy functional groups and an epoxy monomer are described in U.S. Pat. No. 4,547,431 and radiation curable release coatings are described in U.S. Pat. Nos. 4,576,999 and 4,640,967 wherein there is disclosed pre-crosslinked polyorganosiloxane containing units of ##STR2## which R is C.sub.(1-3) alkyl and G is independently C.sub.1-3 alkyl, an epoxy-functional organic radical of 2 to 20 carbon atoms, or an acrylic functional radical of 2 to 20 carbon atoms with at least one unit being epoxy- or acrylic-functional.
U.S. Pat. No. 4,684,709 describes epoxy substituted polysiloxanes and their use as treatment agents for paper, plastic films, etc. having the formula EQU AR.sub.2 SiO(R.sub.2 SiO).sub.x (RQSiO).sub.y SiR.sub.2 A
wherein R is a monovalent hydrocarbon or halogenated hydrocarbon group having from 1 to 10 carbon atoms, A is R or Q, Q is a group with the formula ##STR3##
R.sup.1 is an alkylene group having from 3 to 5 carbon atoms, a has an average value of 0 to 300 and b has an average value of 0 to 30, a+b has an average value of 2 to 60, x has an average value of 1 to 500 and y has an average value of 0 to 100, and containing at least 1 Q group in each molecule.